Significant interest exists in understanding the assembly of primary metal nanoparticles into biodegradable nanoclusters exhibiting intense near-infrared (NIR) extinction. Herein, we present the novel concept of equilibrium gold nanoclusters, in which nanocluster size is tuned by appropriately controlling colloidal interactions with a biodegradable polymer. Nanoclusters are synthesized by mixing a dispersion of primary, ~5 nm Au nanospheres with controlled surface charge with a polymer solution and then evaporating the solvent. Nanocluster size is tuned from 20 nm to 40 nm by varying gold and polymer concentrations. Adsorption of the polymer on the nanocluster surface quenches the nanoclusters at an equilibrium size. Biodegradation of this quencher results in nanocluster dissociation to primary nanospheres. Nanocluster size is predicted semi-quantitatively, using a free energy model which balances short-ranged van der Waals and depletion attractions with longer-ranged electrostatic repulsions. The small interparticle distances within the nanoclusters produce strong NIR extinction ideal for biomedical imaging.

Equilibrium gold nanoclusters quenched with biodegradable polymers

245th National Meeting (2013)

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